Micro-electromechanical systems (“MEMS”) devices have a wide variety of applications and are prevalent in commercial products. One type of MEMS device is a MEMS radio frequency (RF) switch. A typical MEMS RF switch includes one or more MEMS switches arranged in an RF switch array. MEMS metal-to-metal contact RF switches are ideal for wireless devices because of their low power characteristics and ability to operate in radio frequency ranges. MEMS metal-to-metal contact RF switches are well suited for applications including cellular telephones, wireless networks, communication systems, and radar systems. In wireless devices, MEMS RF switches can be used as antenna switches, mode switches, transmit/receive switches, and the like.
Known MEMS switches use an electroplated metal cantilever supported at one end and having an electrical RF metal-to-metal contact near the distal end of the metal cantilever. An actuation electrode is positioned below the electrical RF contact and a direct current (“DC”) actuation voltage applied to either the actuation electrode or the metal cantilever forces the metal cantilever to bend downward and make electrical contact with a bottom RF signal trace. Once electrical contact is established, the circuit is closed and an RF signal can pass through the metal cantilever to the actuation electrode and/or to the bottom RF signal trace.
These MEMS switches typically require 40 V or more actuation voltage. If the actuation voltage is reduce much below 40 V, then the spring constant of the cantilever must be reduced. These lower voltage MEMS switches suffer from “stiction” (i.e., stuck in a closed circuit position) and tend to be self-actuated by RF signals or vibrations due to their low spring constants. During fabrication, the electroplated metal cantilever suffers from high stress gradients and therefore has a tendency to curl upwards at the distal end, referred to as switch stress gradient bending. Accordingly, the actuation voltage must be sufficiently large to overcome the larger separation distance due to beam bending and induce electrostatic collapse between the metal cantilever and the actuation electrode below.